Circumference of wheel to which power is applied,
43"; train of wheels, 25 ÷ 200 × 30 ÷ 180;
circumference of drum on which rope is wound,
14"·9; velocity ratio, 137; mechanical
efficiency, 87; useful effect, 63 per cent.;
formula, _P_ = 0·185 + 0·00782 _R_.
+-----------+--------+--------+----------+--------------+
| | | | P. |Difference of |
| Number of | R. |Observed|Calculated| the observed |
|Experiment.| Load | power | power |and calculated|
| | in lbs.| in lbs.| in lbs. | values. |
+-----------+--------+--------+----------+--------------+
| 1 | 14 | 0·30 | 0·29 | -0·01 |
| 2 | 28 | 0·40 | 0·40 | 0·00 |
| 3 | 42 | 0·50 | 0·51 | +0·01 |
| 4 | 56 | 0·60 | 0·62 | +0·02 |
| 5 | 70 | 0·75 | 0·73 | -0·02 |
| 6 | 84 | 0·85 | 0·84 | -0·01 |
| 7 | 98 | 0·95 | 0·95 | 0·00 |
| 8 | 112 | 1·05 | 1·06 | +0·01 |
+-----------+--------+--------+----------+--------------+
The velocity ratio is now 137, and the mechanical efficiency is 87; one
man could therefore raise a ton with ease by applying a power of 26
lbs. to a crane of this kind.